Multiple frequency signal generator



April 23, 1968 E. Hoo

MULTPLE FREQUENCY SIGNAL GENERATOR Filed oct. la, 1965 INVENTOR. EUGENE HOO BY@ ?Mmm ATTORNEYS United States Patent O 3,379,992 MULTIPLE FREQUENCY SIGNAL GENERATOR Eugene Hoo, Costa Mesa, Calif., assigner to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Filed Oct. 1S, 1965, Ser. No. 496,929 7 Claims. (Cl. 331-2) ABSTRACT F THE DESCLOSURE A means for simultaneously generating a plurality of equally spaced tones in which a frequency divider produces from a signal of frequency fb, a plurality of s-ignals of frequencies f1, f2, f3 fn, each bearing a ratio 1/2x to frequency fb, ywhere x is an integer. Each of a series of signal generating circuits, all arranged in parallel, respond to the signal of frequency fb and to a predetermined one of theA signals of frequency f1, f2, f3 fn to produce an output signal of frequency (fb-Hd), Where fd is the frequency of said predetermined signal and is equal to one of the frequencies f1, f2, f3 fn.

This invention relates generally to multiple frequency signal generating means and, more particularly, to a means for generating a multiplicity of signals whose frequencies are spaced apart by equal frequency differences.

There are in the prior art certain equipments which utilize a multiplicity of signals whose frequencies are spaced equal distances apart from each other. For example, in some communication equipments, such as descri'bed in UnS. Patent 2,905,812 issued Sept. 22, 1959 to M. L. Doelz et al., and entitled, High Information Capacity Phase-Pulse Multiplex System, a plurality of equidistant spaced tones are employed, with one or more channels of information encoded Ion each tone. Due to the particular frequency spacing employed between these tones, it is possible at the receiver to select `any given tone to the almost complete exclus-ion of all the other tones. Such selection of any given tone is possible for the .following reasons. The equidistant spaced tones are passed through a resonator having a resonant frequency equal to the tone which is to be selected. The tone to be selected functions to continually increase the amplitude of resonance of :the resonator, i.e., creates a build-up of energy in the resonator until the energy loss-es within the resonator equal the energy of the input tone. However, those tones which lie outside the resonant frequency of the resonator will at first add energy to the resonator, but then will gradually become out of phase with the energy they have contributed to the resonator and will eventually oppose the energy contributed Ito the resonator. Consequently, the total accumulative energy supplied to the resonator by any frequency outside the selected frequency eventually becomes zero. With the proper selection of frequency spacing between the tones, the zero or nodal point of energy contributed by all tones other than the selected tones can be made to occur at a common point in time. If the tones being supplied to the resonator yare cut off at this common point, then the total energy contribution from all the tones, except the selected tone, is zero, and the only energy remaining in the resonator is that derived from the selected tone.

Many of the prior art schemes for generating multiple frequency signals utilize expensive and complex crystal arrangements in which the frequency of a signal source of stable frequency is divided several times and then recombined with the aid of mixers and filtering arrangements. Other prior art devices employ multiple tones which are built fromv harmonics of the fundamental signal, rather than by dividing the fundamental source signal. Such harmonics are then selected by narrow band- 3,379,992 Patented Apr. 23, 1968 ICC pass filters, which may be networks of crystal filters, and then combined `to form the new desired signal frequencies.

A primary object of the present invention is to provide a relatively simple and inexpensive means for developing a plurality of t-ones spaced apart by equal frequency differences.

A further object of the invention is to provide a means f-or developing a plurality of tones spaced by equal frequency differences in which a complicated network of crystals and crystal filters is not required.

A third purpose of the invention is the improvement of multiple frequency signal generators, generally.

In accordance with the invention, there is provided a high stability standard oscillator source having an output, for example, of 3520 cycles per second, hereinafter designated as fo. It is to be understood that the specific frequencies set forth herein are only for purposes of illustration, and the invention is not limited to such frequencies.

A first frequency divider and a second frequency divider each function to divide the output of the oscilla'tor source. The said first frequency divider divides by a constant factor of 4, for example7 to produce an output signal hav-ing what is herein defined as a base frequency fb; fb in this particular example being 880 c.p.s. The second frequency divider is a binary type frequency divider having six stages, for example, so that it,divides the frequency fo by divisors, e.g.: 21, 22, 23, 24, 25, and 26, to produce output signals having frequencies of 1760 c.p.s., 880 c.p.s., 440 c.p.s., 220 c.p.s., c.p.s., and 55 c.p.s., respectively.

A plurality of individual signal generating circuits are provided; each of said circuits constructed to generate a particular one of a plurality of tones, and compri-sed of a mixer, a phase detector, and a variable controlled oscillator, sometimes herein identified as a VCO. The V'CO of each signal generating circuit has a natural resonant frequency near the desired output frequency of that particular signal generating circuit. For example, it might be desired that ,a particular generating circuit have an output signal frequency of 935 c.p.s. The associated VCO `should have a natural frequency near 935 c.p.s. To obtain an output signal of precisely 935 c.p.s. the output of the said VCO is supplied to the associated mixer along with the 880 c.p.s. signal from said first frequency divider. The difference between the frequency of the tWo signals is 55 c.p.s. Such difference frequency is supplied to the associated phase detector. Als-o supplied to the phase detector is a precise 55 c.p.s. signal from said second frequency divider. If any variation exists between 'the output of the mixer and the S5 c.p.s. signal from said second frequency divider, the phase detector will respond thereto to produce a D-C output of a polarity and a magnitude to correct VCO output frequency until the mixer output is exactly 55 c.p.s. When such condition is obtained, the frequency of the output signal of said VCO will be the desired 935 c.p.s.

Similarly, the other signal generating circuits have VCOs which have natural frequencies near the desired output frequency of such other signal generating circuits.

If it is desired to produce an output signal having a frequency greater than the base frequency of 880 c.p.s. by an amount not obtainable directly from any single tap of said second frequency divider, the output signals from 'two or more taps of said sec-ond frequency divider can be mixed to produce the desired incremental frequency. `For an example, to produce an output signal of 1045 c.p.s., -it is necessary to supply, to the phase detector of the proper signal generating circuit from the second frequency divider, a signal having a frequency of c.p.s., since 1045-880=165. To obtain such a signal from the second frequency divider, it is necessary to add together the 55 c.p.s. output signal and the 110 c.p.s. output signal. Such addition can be performed in a suitable mixer circuit.

The above-mentioned and other objects and features of the invention will be more fully understood from the following detailed description thereof when read in conjunction with the single drawing which shows a schematic sketch of the invention.

As indicated above, to facilitate an explanation of the invention a denite set of frequencies will be employed. However, it is to be noted that many different combinations of frequencies can be employed in the invention other than the one that is used herein.

In the drawing, the high stabity, standard oscillator source supplies an output signal of a frequency of 3520 c.p.s. to frequency divider 14 and also to frequency divider 11. The frequency divider 14 functions to divide the output of the oscillator by 4 to produce a signal having a base frequency fb (880 c.p.s.) an output lead 9. The output lead 9 is connected to an input of mixers 15, 18, 20, and 25, each of which comprises a portion of the circuits within blocks 49, 50, 51, and 52, respectively.

The frequency divider 11 also responds to the output of oscillator source 10 to produce a plurality of output signals whose frequencies are equal to the output frequency fo of standard oscillator 10 divided by an integer. More specilically, the frequency divider 11 is a binary frequency divider and divides the output of the oscillator 10 by powers of 2. Such powers of 2 result in divisors of 2, 4, 8, 16, 32, 26 2n, where n is the number of stages of frequency divider 11. In the particular example shown, the frequency divider 11 has six stages so that the largest divisor of output frequency fo of source 10 is 26, to produce a 55 c.p.s. signal on output lead 49 of frequency divider 11.

Returning again to the generating circuits within blocks 49, 50, 51, and 52, it is to be noted that the circuit within each block is constructed to produce a tone of a particular frequency on output leads 45, 46, 47, and 48, respectively. For example, the circuit Within block 49 is constructed to produce an output signal on output lead 4S of 935 c.p.s. The circuit within block 50 produces an output signal of 990 c.p.s.; and the circuits within blocks 51 and 52 output signals of frequencies 1045 c.p.s. and 1100 c.p.s., respectively. Each of the circuits 49 through 52 produces the aforementioned output signals in response to the two signals provided thereto from frequency divider 14 and frequency divider 11.

Consider the operation of the cirucit of block 49 as a specific example. Within block 49' is a mixer 15, a phase detector 30, a variable controlled oscillator 16, and an amplifier 40. The VCO 16 is constructed to have a free running frequency near the desired output frequency of 935 c.p.s. The output signal of frequency divider 14, which has a frequency of 880 c.p.s., is supplied to mixer 15. The output of VCO 16, which has a frequency of near 935 c.p.s., also is supplied to mixer 15. Mixer 15 responds to the two signals supplied thereto to produce an output signal on output lead 51 having a frequency near 55 c.p.s. A precise 55 c.p.s. signal from frequency divider 11 is also supplied to phase detector 30 through leads 49 and 13. Phase detector 30 responds to the two frequencies supplied thereto to produce a D-C signal on its output terminal 52, having a polarity and a magnitude indicative of the direction and degree of change required in the frequency of the output signal of VCO 16 to correct said VCO output signal to a precise 935 c.p.s. frequency. When the VCO output frequency is corrected to 935 c.p.s., the output signal of mixer circuit 1S will have a frequency of exactly 55 c.p.s., which frequency will be supplied to phase detector 30 via lead 51. When such condition is obtained, the output of phase detector 30 will be substantially zero D-C volt and the correction of VCO 16 will have been completed.

In a similar manner, frequency control of VCO 17, VCO 22, and VCO 27 in the circuits within blocks 50, 51, and 52 is obtained. It is to be noted, as indicated above, that the output signal of block 50y has a frequency of 990 c.p.s.; the output of block 31, a frequency of 1045 c.p.s.; and the output of block 52, a frequency of 1100 c.p.s. It will further be observed that the difference in frequency between the outputs of blocks 49, 50, 51, and 52 is 55 cycles per second. This particular frequency spacing is chosen to allow the nodal point, or zero energy point, of all the tones generated therein (except the selected tone) to occur at the same time in a receiver resonator circuit, as discussed in the aforementioned U.S. Patent 2,905,812.

In some instances, the signal taken from any single output of frequency divider 11 cannot be employed to produce the desired output signal within one of the blocks 49 through 52. More specifically, assume that it is desired to produce the 1045 c.p.s. tone signal within block 51. Since the difference between 1045 c.p.s. and the 880 c.p.s. signal from divider 14 is 165 c.p.s., it is not possible to derive the 1045 c.p.s. signal by utilizing any single output of frequency divider 11. Worded in another way, it is necessary to supply a c.p.s. signal from frequency divider 11 to phase detector 21 in order to maintain and phase lock the 1045 c.p.s. signal in VCO 22. To obtain such a 165 c.p.s. signal, the output signals from terminals 49 and 58 of frequency divider 12 are mixed in a suitable mixer circuit 23 and the output thereof supplied t0 a narrow bandpass filter 24. The filter 24 is constructed to pass a 165 c.p.s. signal 0btained by adding together the 55 c.p.s. signal and the 110 c.p.s. signal from output terminals 49 and 58 of frequency divider 11.

Thus, the output signal of VCO 22, which in its free running state is somewhere near 1045 c.p.s., will be supplied to mixer 20 and will mix with the 880 c.p.s. signal from divider 14 to produce at its output terminal 60 a signal having a frequency near 165 c.p.s. The phase detector 21 will compare such signal with the precise 165 c.p.s. signal received from filter 24 to produce a D-C voltage which will correct the VCO 22 to precisely 1045 c.p.s.

While only four signal generating circuits 49, 50, 51, and 52 are shown in the drawing, it is to be understood that others can be added to the system. As one example, the 440 c.p.s. output and the 1760 c.p.s. output from frequency divider 11 could be added together to produce a signal having a frequency of 2200 c.p.s. Such 2200 c.p.s. signal could then be employed to produce an output signal having a frequency of (2200+880) or 3080 c.p.s. Other combinations will be readily apparent to one skilled in the art.

Ampliiiers 40, 41, 42, and 43 are provided merely to amplify the outputs of VCOs 16, 17, 22, and 27 to a level suitable for a desired load utilization.

It is to be understood that the form of the invention shown and described herein is but a preferred embodiment thereof and that various changes may be made in the circuit arrangement and in frequencies employed without departing from the spirit or scope of the invention.

I claim:

1. Multiple tone generating means comprising:

rst signal generating means for generating a signal of frequency fb;

first frequency divider constructed to respond to a first output signal of frequency 2 Y1 fb of said iirst signal generating means to produce a plurality of second output signals of frequencies f1, f2, f3, fn, where n is determined by the construction of said frequency divider means and where Y is an integer;

a plurality of signal producing circuits connected in parallel arrangement with respect to the output signal of frequency fb of said first signal generating means, and each comprising:

mixer circuit means;

phase detector means; and

variable controlled oscillator means having output means; the mixer means of a given signal producing circuit responsive to the signal of frequency fb and the output signal of frequency fvco of the variable controlled oscillator of said given signal producing circuit to produce a second output signal of frequency (fb-.fvco); i

said phase detector means responsive to Said signal of frequency (fb-fm) and to a predetermined one of said second output signals of frequency f1, f2, f3 fn supplied thereto to produce an error output signal indicative of the phase relation between said signal of frequency (fb-fm) and said predetermined one of said second output signals of fre quency fd, where fd is one of the frequencies f1, f2, .f3 fn;

said variable controlled oscillator responsive to said error output signal to change the frequency of its output signal of frequency fvco to a desired frequency equal t0 (fblfd) 2. Multiple tone generating means in accordance with claim 1 in which:

said first frequency divider means is a binary counter with output means from selected stages to produce signals of the frequencies f1, f2, f3, fn, each of which frequencies bears ratio 1/2x to the frequency fb, where X is an integer.

3. Multiple tone generating means in accordance with claim '2 comprising:

means for combining selected ones of said signals of frequencies f1, f2, f3, fn to prod-uce resultant output signals of frequencies equal to the sums and differences of said selected signals;

and in Iwhich selected ones of said signal producing circuits are each constructed to respond to a selected one of said resultant output signals and the signal of frequency fb to produce an output signal of a frequency equal to frequency fb plus the frequency of said resultant output signal.

4. Multiple tone generating means in accordance with claim 1 in which said first signal generating means comprises:

stable oscillator means having an output signal of frequency 2er-ufo;

and second divider means for dividing the output signal of said oscillator means by a factor 2m, where m is an integer, to prod-nce said signal of frequency fb.

5. Multiple tone generating means in accordance with claim 4 comprising:

means for combining selected ones of said signals of frequencies f1, f2, f3, fn to produce resultant output signals of frequencies equal to the Sums and differences of said selected signals;

and in which selected ones of said signal producing circuits are each constructed to respond to a selected one of said resultant output signals and the signal of frequency fb to produce an output signal of a frequency equal to frequency fb plus the frequency of said resultant output signal.

6. Multiple tone generating means comprising:

first signal generating means for generating a first signal of frequency fb;

frequency divider means comprising a binary counter means having a plurality of stages with output means at selected stages thereof and constructed to respond to fan output signal of frequency 2,(Y-Ufb of the first signal generating means to produce a plurality of second output signals of frequencies f1, f2, f3 fn at said output means, and where n is determined by the construction of said first frequency divider means, where Y is an integer; and where each of said frequencies f1, f2, f3 fn bears the ratio l/ 2X to said frequency 2(Y1)fb, with x being an integer;

a first plurality of signal producing circuits each constructed to respond to said signal of frequency fb Iand a signal of frequency fd derived from at least one of said signals of frequencies f1, f2, f3, fn to produce an output signal of frequency (fb-Hd);

means for mixing selected ones of said signals of frequencies f1, f2, f3, fn to produce resultant output signals of frequencies equal to the sum and differences of said selected signals;

and a second plurality of signal producing circuits each constructed to respond to a selected one of said resultant output signals and the signal of frequency fb to produce an output signal of a frequency equal to frequency fb plus the frequency of said selected resultant output signal.

7. Multiple tone generating means comprising:

first signal generating means for generating a signal of frequency fb;

frequency divider means constructed to respond to a first output signal of frequency 2(Y1)fb of the first signal generating means to produce a plurality of second output signals of frequenciesnfl, f2, f3, fn, Where N is determined by the construction of said frequency divider means, Where Y is an integer, and where each of the frequencies f1, f2, f3, fn bears a ratio 1/2x to the frequency fb being an integer;

a plurality of signal producing circuits;

selected ones of said signal producing circuits each being constructed to respond to said signal of frequency fb and a signal of frequency fd derived from at least one and to one of said signals of frequencies f1, f2, f3, n to produce an output signal of a frequency (fb-l-fd), where d is one of the frequencies .fh f2 f3 fn;

and means for combining selected ones of said signal frequencies f1, f2, f3 fn to produce resultant output signals of frequencies equal to the sums and differences of said selected signals;

other selected ones of said signal producing circuits each being constructed to respond to one of said resultant output signals and the signal of frequency fb to produce an output signal of a frequency equal to fb plus the frequency of said one of said resultant output signals.

References Cited UNITED STATES PATENTS 3,202,930 8/ 1965 Muraszko 331--2 3,212,024 10/1965 King 331-38 X 3,293,561 12/1966 Hegarty et al. 331-38 ROY LAKE, Primary Examiner.

I B. MULLINS, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTHHCATE 0F CORRECTHM Patent No. 3,379,992 April 23, 1968 Eugene Hoo It is certified that error appears in the above identified patent and that said Letters P atent are hereby corrected as' shown below:

Column 4, line 72, after "said" insert first Column 5, line 49, "fo" should read fb Column 6, line 38, after "frequency fb," insert with x line 44, "n" should read fn line 4S, "where d" should read where fd Signed and sealed this 2nd day of December 1969.

(SEAlJ fittest:

Edward M. Fletcher, Jr.

WILLIAM E. SCHUYLER, JR. Attesting Ufficer Commissione; of Patents 

